1. Field of the Invention
The present invention relates to a percussion electrical hand-held tool such as trepan or a chisel power tool for working stone materials.
2. Description of the Prior Art
In the electrical hand-held tools of the type described above, an axial impact energy, which is generated by a percussion mechanism is transmitted to percussion working tool for working a workpiece. A portion of the energy, through the handle, acts on a tool user, causing disturbing vibrations in the user hand.
A large press-on force, which is applied to the handle, is associated, in percussion hand-held tools, with an intuitive desire to increase the break-down output. Contrary to that, in pure rotary tools, an increase press-on force leads to reduction of the rotational speed. Power parameters of a break-down work include, in particular, impact power, impact frequency, and optionally, rotational speed of the percussion power tool.
German Publication DE-19649468 discloses an electrical hand-held tool with control means being provided in the guide handle or in the auxiliary handle.
German Publication DE-3843960 discloses controlling an operation of control electronic of an electrical hand-held tool by a functional potentiometer with a pressure pad.
German Publication DE-19510365 discloses the use, in a functional potentionmeter, of a compressible medium in form of a fluid that is provided in the control member between a pressure plate and a sensor for transmitting pressure.
U.S. Pat. No. 4,250,434 discloses the use of a pressure-sensitive electrical sensor, which is formed as a flexible pressure hose, for controlling a machine.
German Publication DE-19703746 discloses an arrangement of a damping element on the rear gripping surface of a handle of an electrical hand-held tool.
U.S. Pat. No. 5,987,705 discloses a handle with a pressure sensor which controls a pump for generating a vibration suppressing inflation pressure.
German Publication DE-3316013 discloses a hammer drill with a control member or servo component arranged on the tool housing for steplessly controlling an impact energy of the hammer drill.
In German Publication DE-4231986, a mechanical control of the coupling of the percussion mechanism of a hammer drill is effected by using a press-on force applied by the power tool to a workpiece. However, the necessary, movable relative to each other and slidable on each other, parts cannot be used in the rough environment of the constructional industry, as the penetrating dust reduces the operational reliability of such electrical tool.
An object of the present invention is to provide a sliding movement-free, intuitive control of a power parameter, in particular, of an axial impact energy of a percussion electrical hand-held tool.
Another object of the present invention is to prevent transmission of vibration to a tool user hand.
These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a percussion electrical hand-held tool including an electronic control unit for controlling at least one power parameter of the electrical tool, and a pneumatic force sensor for controlling operation of the electronic control unit and arranged, free of sliding displacement, for sensing a press-on force applied by a user in an operational direction of the electric tool between at least two, associated with each other, press-services extending at least partially transverse to a percussion axis of the electrical tool.
The arrangement of the force sensor, according to the present invention, between associated press-surfaces for a displacement-free sensing of a press-on force for controlling a power parameter, can be safely used even in a rough environment.
Advantageously, the pneumatic force sensor is formed as a hollow pneumatic force transmission member connected with a force sensing element connectable with the electronic control unit.
Advantageously, the force transmission member is filled with an easily deformable, pressure transmitting medium or a fluid, pressure transmitting medium, e.g., pneumo-oil, gel, or high viscouls solid non-free flowing, non-evaporating material.
Advantageously, the hollow pneumatic force transmission member is formed as a cushion or hose the cross-section of which becomes compressed upon application of press-on force, and becomes deformed, which increases the hydrostatic pressure of the pressure transmitting medium.
Advantageously, the force sensor is located in a front section of the tool, behind an axial position of the tool chuck or behind the spindle bearing, which permits to measure the entire press-on force.
Advantageously, the force transmission member extends up to the handle, which makes possible to measure the entire press-on force acting on the force sensing element in the handle.
Advantageously, the press-surfaces are arranged, with respect to a force flux, between the percussion mechanism and a gripping surface of the handle.
More advantageously, the press-surfaces are arranged in a region of working tool-side, axial position of the percussion mechanism relative to a tool outer casing of which the handle forms a part, or in a region of a modular position of a drive module and a handle module.
Advantageously, the force transmission member extends transverse to the percussion axis and is arranged between the handle and a vibration-proof grripping casing, whereby the vibration in the pressure transmission medium are damped and are prevented from being transmitted to the user hand.
Advantageously, the tool side handle is also provided with a force-sensor forming, force transmission member provided with a force sensing element electrically connected, via signal conductors, with the force sensing element in the handle, whereby the sum of press-on forces of both the handle and the side handle are used for control purposes.
Alternatively, the force transmission member of the side handle can be connected directly with the force transmission element in the handle, which permits to use a common force sensing element, without the use, in the front portion of the power tool, current conducting conductors, which eliminates the safety problems associated with such conductors.
Advantageously, there is provided a low-pass filter with a cut-off voltage of less than 30 Hz between the control unit and the force sensor. The low-pass filter filters out the low frequency control signals and suppress the high frequency vibrations.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment, when read with reference to the accompanying drawings.